International Business Systems (IBM) developed the Intersystem Channel (ISC) data format for transmitting data between computers. The inventors herein have recognized that is would be advantageous to encapsulate ISC words in Generic Framing Procedure (GFP) frames for transmitting the ISC words over a synchronous optical communication network (SONET). A problem associated with the transmitting ISC words from a first computer through the SONET communication network to a second computer is that repeating devices disposed between the first and second computers may have different clock speeds than the first computer. When a data mapping device for encapsulating the ISC words in a GFP frame has a different clock speed than the first computer, either an over-running condition or an under-running condition can occur.
An over-running condition occurs when a transmission rate of ISC words received from the first computer by the data mapping device is greater than a transmission rate of the ISC words from the data mapping device. If the over-running condition is not addressed, an internal storage buffer within the data mapping device can overflow and ISC words can be lost during transmission from the first computer to the second computer.
An under-running condition occurs when a transmission rate of the ISC words received from the first computer by the data mapping device is less than a transmission rate of the ISC words from the data mapping device. If the under-running condition is not addressed, an internal storage buffer within the data mapping device will not have sufficient ISC words to be transmitted through the SONET communication network.
Accordingly, there is a need for a data mapping device and a method for adjusting a transmission rate of ISC words therefrom to minimize or eliminate the under-running condition and the over-running condition.